Hi there susanmquesnel-gm,
Thanks for reaching out about your invoices. QuickBooks Online is a great tool able to help you create and send invoices so your customers know the balance they owe for your services. I can provide some information about attachments.
When you add an attachment to the attachments section of an invoice, it isn't sent with the invoice itself, unless you check the box that you want to send it with the invoice. Make sure to check the box to make sure it's selected to be sent with the invoice.
If you have any other questions, feel free to reach out here.